Multiplet-changing Auger transitions in valence double photoionization

Abstract

The decay of valence satellite states in neon above the first double-ionization threshold has been studied experimentally and theoretically. Special emphasis was given to differentiate between two decay modes: valence Auger and valence-multiplet Auger decay. It is shown that the latter process is predominant in the low kinetic energy part of the spectrum. The main structures of this low-energy Auger spectrum could be designated by help of calculated transition energies and decay rates.PACS number(s): 32.80.Fb, 32.80.Hd, 32.80.0z, 33.60.Cv Double ionization of valence shells in atoms and molecules has recently attracted considerable interest [l -3].The reason for this recovered, still increasing interest is due to the existence of a delicate balance of competing processes contributing to the valence-shell double ionization. These processes are known as simultaneous and sequential or direct and indirect processes. Whereas the first experiments on double ionization assumed almost all intensity of doubly charged ions resulting from singlephoton ionization as due to a simultaneous or direct double-ionization process, the so-called shakeoff process, the more recent studies showed that this is not true: sequential or indirect processes contribute significantly to the valence double-ionization rate [4 -6]. Since that time, experimental and theoretical studies have tried to explore this phenomenon in more and more detail. Armen and Larkins [7] were the first to our knowledge who showed on the basis of neon data from Becker et al. [4] that the sequential processes split into two distinct decay modes: inner-valence and valence multiplet-changing Auger transitions. In both cases the excited electron does participate in the transition process, corresponding to decays where the excited core changes either its electronic configurations [for instance, Ne+ 2s2p ( P)np( S) Ne + 2s 2p ('S+'D)+e ] or its multiplet coupling [such as Ne 2s 2p ('S)np( P)~Ne + 2s 2p ( P) +e ], for example, in a spin-fiip process, using hypothetical one-electron levels for the sake of simplicity. Figure 1 shows the different processes schematically for the case of neon. The theoretical and experimental interest is focused on the latter process for two reasons: (i) its high transition probability, and (ii) the occurrence of electrons with very low kinetic energy.The valence multiplet-changing transition, also referred to as nonresonant autoionization, may, in the extreme, give rise to the ejection of 0-V kinetic energy Auger electrons. Figure 2 shows a complete electron spectrum of neon taken at a photon energy of hv=120 eV exhibiting clear evidence for all three processes: simultaneous double ionization, inner-valence Auger transitions, and valence multiplet-changing Auger transi-Valence Auger Valencemultiplet Auger 3s I zrrnzizz nI', '/( 8/ /// / AX/8 / 'il it' 2p n iL / / / / / / / /, // 2s C FIG. 1. Simplified schematic representation of neon inner-valence 2s photoionization with accompanying excitation together with possible subsequent recombin...

Coherence and correlations in photoinduced Auger and fluorescence cascades in atoms

“…Similarly, the rank of the tensor cannot be larger than 2 (in dipole approximation). Usually, the alignment A 2q ( 0 J 0 ) of the photoions is small (about 0.1) for all photon energies except in the near-threshold region and in the region of Cooper minimum (Berezhko et al, 1978a;Kleiman and Lohmann, 2003). In contrast, circularly polarized light can produce also an orientation of the photoion, i.e.…”

“…Similar to the experiments on the angular distribution of photoelectrons, the fluorescence intensity is determined hereby at two observation angles with respect to the polarization vector of the exciting linearly polarized synchrotron radiation, typically at = 0 • and 90 • . The alignment parameter A 20 (J ) is then obtained in the standard way by using expression (41) of Section 3 (Berezhko and Kabachnik, 1977;Balashov et al, 2000). This method was applied, for instance, in experiments using SR beam-lines at BESSY I and II in Berlin delivering rotatable linear polarization of the exciting photons, which makes it possible to perform experiments at a fixed spectrometer geometry Schmoranzer et al, 1997;Ehresmann et al, 1998;Demekhin et al, 2005).…”

“…A kq ( 0 J 0 ) ∼ q0 , the angular distribution depends only on the angle ϑ between the symmetry axis and the linear momentum of the ejected electron (Berezhko and Kabachnik, 1977;Kabachnik and Sazhina, 1984):…”

“…in the decay of the resonance state A * ( 0 J 0 ), their angular distribution can be written in the general form (Berezhko et al, 1978b;Balashov et al, 2000, Eq. (3.10))…”

Dynamics of electron emission in double photoionization processes near the krypton 3d threshold

“…Initially, the VMD effects were investigated in the decay rates of valence shake-up states of Ne and Ar (Becker et al 1989, Armen and Larkins 1991, Becker et al 1993. An important role of VMD has been revealed in the threshold electron spectra , Sheinerman et al 2006 and in the population of the highly excited Rydberg states (De Fanis et al 2004, Kitajima et al 2006.…”